A conventional thin torque converter a type of fluid coupling, is shown in FIG. 3. This converter, indicated by numeral 1', has a pump impeller 3 connected with an input member 2, a turbine runner 6 connected with an output member 5, and a stator 7 located in the oil path between the runner 6 and the impeller 3. The stator 7 is connected and held to a stationary member via a one-way clutch 9.
This one-way clutch 9 comprises an outer race 10, an inner race 11, sprags 12 forming wedge members located between the outer race 10 and the inner race 11, and two thrust washers 13, 14. The stator 7 has a boss 7a over which the outer race 10 is fitted. The inner race 11 is connected with the stationary member via a sleeve shaft. The washers 13 and 14 are held between thrust bearings 15 and 16 such that the outer race, the inner race, and the sprags are sandwiched between these washers.
The outer race 10 of this conventional construction has side end surfaces 10a' which are flat in the same way as the inner race 11. The thrust washers 13 and 14 extend straight radially outwardly along the flat end surfaces 10a' to form flat plate portions 13a and 14a, respectively. Snap rings 17 and 19 which are fitted over the boss 7a of the stator prevent the flat plate portions 13a and 14a from coming off.
When the one-way clutch 9 is free to rotate, the outer race 10 rotates relative to the inner race 11. In this state, the protruding portions 13b and 14b of the thrust washers 13 and 14 are fitted between the races 10 and 11 to prevent the sprags 12 from rolling over or popping out. At this time, the thrust washers 13 and 14 rotate with the outer race 10. These washers provide a large surface area in contact with the inner race 11. When the clutch is locked, the sprags 12 exert a large radially outwardly directed force and a large shearing force on the outer race 10. These forces are received by the flat end surfaces 10a' of the outer race 10. Hence, the clutch has sufficient durability.
Although the one-way clutch 9 described above performs desired functions and has desired durability, the width of the outer race 10, the thicknesses of the two thrust washers 13, 14, and the thicknesses of the snap rings 17 and 19 together form the axial dimension of the clutch. Thus, the axial dimension is increased. Also, the weight is relatively large. As a result, it is impossible to make the torque converter 1' thinner and lighter in weight.